feat(cost-model): migrate adv-stats

[xx01cyx]

In optd, we use MostCommonValues and Distribution as trait bounds. Because of the serialization & deserialization need in optd-persistent, we use concrete types (enum) here instead of traits.

[skyzh]

I would rubber-stamp all patches in this repo to ensure we move fast but I'd like to note that

• Would be better to have an initial commit to copy-paste everything from the optd repo, and another commit which contains the changes to the original crate. Otherwise I don't know what changes I'll need to review :(
• Would be better if we can bring all commit history to this repo.

Looking at the dependencies, I saw lazy_static being used, which is already a deprecated crate and replaced by std libraries once cell. Probably needs to be fixed?

Regarding enum -- I'm not sure if this is a good approach regarding extensibility but let's merge it as-is.

[xx01cyx]

Would be better to have an initial commit to copy-paste everything from the optd repo, and another commit which contains the changes to the original crate. Otherwise I don't know what changes I'll need to review :(

Sure. This is actually separated from another larger PR. I just copy-pasted all code... I'll do so next time.

Would be better if we can bring all commit history to this repo.

Is there a good way to do so?

Looking at the dependencies, I saw lazy_static being used, which is already a deprecated crate and replaced by std libraries once cell. Probably needs to be fixed?

I've added a TODO in the code.

Regarding enum -- I'm not sure if this is a good approach regarding extensibility but let's merge it as-is.

I've tried to make MostCommonValues and Distribution as traits, but doesn't work out very well. Not sure if there's a better solution.

[skyzh]

https://git-scm.com/docs/git-filter-branch + git merge from an orphan branch